Using Program MARK and a Modified Minimum Number Alive to Estimate Survival, Capture Probabilities, and Population Trends in Two Subpopulations of Ornate Box Turtles (Terrapene ornata ornata) in Eastern Iowa

Ornate box turtles (Terrapene ornata) are a threatened species in Iowa due primarily to prairie habitat loss. We analyzed data from a 21 year mark-recapture study to assess the survival of ornate box turtles in two subpopulations at Hawkeye Wildlife Area in Johnson County, Iowa. We used Program MARK to generate estimates of survival and capture probabilities at each site. We then used the capture probabilities in a modified Minimum Number Alive (MNA) to estimate the population size at each site during each year of the study.

When we put a constant capture probability into the modified MNA model, it showed that the population at Mallard Pools was stable and the population at Greencastle was declining. When we used MARK to generate population estimates using time and site dependent capture probabilities from the Cormack-Jolly-Seber (CJS) model, the population estimates were similar to those from MNA, but the populations at both sites appeared stable.

Since the MARK analysis found that capture probability varies significantly between years and between sites, we decided to run the MNA analysis again with the capture probability estimates from MARK. We then compared these population estimates to those found using a constant capture probability with MNA and those found using the CJS model. We found that CJS was less reliable than MNA. From this we can conclude that our hypothesis that Mallard is stable and GC is declining was supported.